Palisade
<p>
Draw lines along the grid edges, in such a way that the grid is
divided into connected regions, all of the size shown in the status
line. Also, each square containing a number should have that many of
its edges drawn in.
<p>
Click on a grid edge to mark it as a division between regions (black),
and again to return to marking it as undecided (yellow). Right-click
on a grid edge to mark it as definitely not part of the loop (faint
grey), and again to mark it as undecided again.
